One example of D/A converters for converting a digital signal into an analog signal is an R-2R type D/A converter using a ladder type resistor network.
As illustrated in FIG. 24, the R-2R type D/A converter includes a resistor network 301 and three switches 302 to 304 corresponding to digital input signals D0 to D2. Respective switches 302 to 304 include transistors 302a to 304a coupled between a wiring 311 at a high potential voltage VD level and the resistor network 301 and transistors 302b to 304b coupled between the resistor network 301 and a wiring 312 at a low potential voltage GND level. The transistors 302a to 304 and 302b to 304b are complementarily turned on and off according to the digital input signals D0 to D2.
The R-2R type D/A converter outputs an analog signal VOUT having a voltage value obtained by dividing a voltage difference between a high potential voltage VD and a low potential voltage GND by ON-resistances of resistance elements included in the resistor network 301 and the respective transistors 302a to 304a, 302b to 304b. For example, the R-2R type D/A converter outputs an analog signal VOUT having a voltage value corresponding to a code (decimal number) and the digital input signals D2 to D0 as illustrated in FIG. 25. In FIG. 25, the voltage value of the analog signal VOUT indicates a case where the high potential voltage VD=6.4V and the low potential voltage GND=0V. The code represents binary numbers represented by the digital input signals D0 to D2 in the form of a decimal number.
There is demand for D/A converters to correspond to multi-bit digital input signals to increase resolution. For example, a case of an R-2R type D/A converter is illustrated in FIG. 26. Another D/A converter includes a first-stage D/A conversion unit for generating a voltage corresponding to a high-order bit of a digital input signal and a next-stage D/A conversion unit for generating a voltage corresponding to a low-order bit of a digital input signal based on an output voltage of the first-stage D/A conversion unit. Reference is made, for example, to Japanese Laid-Open Patent Publication Nos. 2003-224477 and 5-248028 and Japanese Examined Patent Publication No. 63-6170.